Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device that can be positioned behind the panel so that the touch-sensitive surface can substantially cover the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
When using a touch screen, a user can make a selection on the display screen by pointing directly to objects (such as GUI objects) displayed on the screen (usually with a stylus or finger) and touching the screen at that location. To provide additional functionality, gesture recognition can be implemented to recognize more than a simple finger touch. By way of example, various operations such as a selection function can be made when one or more taps are detected on the surface of the touch screen. In addition to taps, various operations such as dragging or scrolling functions can be made when a sliding motion is detected on the surface of the touch screen. Tapping and sliding gestures are described in Applicant's co-pending U.S. patent application Ser. No. 11/818,341 entitled “Detecting Gestures on Multi-Event Sensitive Devices,” filed on Jun. 13, 2007 the contents of which are incorporated by reference herein.
However, it can be difficult for a user to control finger motion to produce a tapping motion with little or no sliding motion. Tapping gestures with some amount of sliding motion, so-called “sloppy taps,” can be difficult to distinguish from a true sliding gesture as intended by the user.
The problem of distinguish sloppy taps from sliding motions can pose contradictory objectives: reliably producing clicks (e.g. selection operations) in response to sloppy taps that including some amount of finger sliding or rolling motion, versus issuing point/drag/scroll events quickly enough in response to intentional slides such that the user perceives little or no lag or lost motion. Some touch sensor panel systems have attempted to distinguish sloppy taps from sliding motions by suppressing all motion or a percentage of finger motion for a certain period of time (e.g. several hundred milliseconds) after a touch event was detected. However, such approaches can lead to excessive suppression of intended sliding motions, especially for quick sliding motions of a short duration.